This invention relates to high frequency oscillators, and more particularly, to a high frequency oscillator having complementary multi-phase outputs.
In the data communications field, there are many applications for a multi-phase oscillator with complementary outputs. For example, a nine stage oscillator would produce at the oscillator frequency nine six multi-phase output signals phased 40, 80, 120, 160, 200, 240, 280, 320, and 360 degrees from each other. But each stage adds delay. Thus, generally the more stages there are, the slower is the oscillator and the lower is the maximum frequency of the oscillator. Complementary outputs can be generated by using differential stages or inverting single-ended outputs. However, both of these measures slow the oscillator operation and load the circuitry.
According to the invention, an oscillator having multi-phase complementary outputs comprises a first plurality of single ended amplifiers connected in series to form an input and an output and a second plurality of single ended amplifiers connected in series to form an input and an output. The first and second plurality have the same odd number of amplifiers. A first feedback path connects the output to the input of the first plurality of amplifiers to establish oscillations in the first plurality of amplifiers at a frequency dependent upon the delay time from the input to the output of the first plurality. A second feedback path connects the output to the input of the second plurality of amplifiers to establish oscillations in the second plurality of amplifiers at a frequency dependent upon the delay time from the input to the output of the second plurality. A first locking circuit is connected between comparable first points in the first and second plurality of amplifiers to ensure that the first points are oscillating in complementary fashion and a second locking circuit is connected between comparable second points in the first and second plurality of amplifiers to ensure that the second points are oscillating in complementary fashion.